Recently, there has been a demand for downsizing a semiconductor device that is used for a portable electronic device such as a mobile phone or a nonvolatile record media of an IC memory card. As such, there is a demand for packaging a semiconductor element efficiently. There exists an art in which a semiconductor element is stacked and is packaged.
A description will be given of a first through third conventional embodiments as an example of the art where the semiconductor element is stacked and is packaged. A description will be given of a semiconductor device in accordance with the first conventional embodiment, with reference to FIG. 1. As shown in FIG. 1, the semiconductor device in accordance with the first conventional embodiment has mainly a substrate 10, a semiconductor element 14 and a built-in semiconductor device 48.
The built-in semiconductor device 48 has a substrate 12, a semiconductor element 18, a die attach 22, a wire-connecting pad 34, a wire 32 and a molding portion 24. The semiconductor element 18 is die-bonded to the substrate 12 and the semiconductor element 18 is electrically coupled to the substrate 12 through the wire 32 made of gold (Au). The semiconductor element 18 is enclosed by a molding portion 24. The molding portion 24 is formed with an epoxy resin or the like.
A wire-connecting pad 34 made of Au, Cu (copper) or the like, a pad 40 for flip-chip connecting, an electrode-connecting portion 36 and a land electrode 38 on the substrate 10 made of glass epoxy or the like are each formed. A solder ball 42 as a connecting terminal is coupled to a lower surface of the substrate 10. The semiconductor element 14 made of silicon or the like is mounted on the substrate 10. The semiconductor element 14 is electrically coupled to the substrate 10 with a bump 46 made of Au, Cu or the like. A space between the substrate 10 and the semiconductor element 14 is filled with an under fill 44 made of epoxy resin or the like. The semiconductor element 14 is enclosed by a molding portion 28. The molding portion 28 is formed with an epoxy resin or the like. The built-in semiconductor device 48 is fixed to the molding portion 28 with a fixing agent, forming a fixing portion 20. The built-in semiconductor device 48 is electrically coupled to the substrate 10 with a wire 30 made of Au or the like. The built-in semiconductor device 48 and the molding portion 28 are enclosed by a molding portion 26. The molding portion 26 is formed with an epoxy resin or the like.
A description will be given of a semiconductor device in accordance with the second conventional embodiment with reference to FIG. 2. As shown in FIG. 2, the semiconductor device in accordance with the second conventional embodiment includes: a substrate 10, a semiconductor element 14, a semiconductor element 14a and a built-in semiconductor device 48. In FIG. 2, there is provided a semiconductor element 14a, the height of which is different from that of the semiconductor element 14. Also, the molding portion 28 shown in FIG. 1 is not formed in the case of FIG. 2.
A description will be given of a semiconductor device in accordance with the third conventional embodiment with reference to FIG. 3. As shown in FIG. 3, the semiconductor device in accordance with the third conventional embodiment includes the substrate 10, the semiconductor element 14 and a built-in semiconductor device 52. The semiconductor element 14 is mounted on the substrate 10. The built-in semiconductor device 52 is mounted on the semiconductor element 14. The built-in semiconductor device 52 is electrically coupled to the substrate 10 with a solder ball 68.
The built-in semiconductor device 52 has a substrate 50, a semiconductor element 58, a semiconductor element 60, a die attach 62, a die attach 64, the wire-connecting pad 34, a wire 54, a wire 56, the land electrode 38, the electrode-connecting portion 36 and a molding portion 66. The semiconductor element 58 and the semiconductor element 60 are die-bonded to each other with the die attach 64. The substrate 50 and the semiconductor element 58 are die-bonded to each other with the die attach 62. The substrate 50 and the semiconductor element 58 are electrically coupled to each other with the wire 56 made of Au or the like. The substrate 50 and the semiconductor element 60 are electrically coupled to each other with the wire 54 made of Au or the like. The semiconductor element 58 and the semiconductor element 60 are enclosed by the molding portion 66. The molding portion 66 is formed from an epoxy resin or the like. The same components have the same reference numerals as in FIG. 1 and FIG. 2 in order to avoid a duplicated explanation.
Japanese Patent Application Publication No. 2003-282814 (hereinafter referred to as Document 1) discloses a semiconductor device in which an entire semiconductor element is enclosed by an epoxy resin or the like. The invention shown in Document 1 is characterized in that the entire semiconductor element is enclosed and any damage to the semiconductor element is minimized.
In the semiconductor device in accordance with the first conventional embodiment, the upper surface of the semiconductor element 14 is enclosed by the molding portion 28. The height of the semiconductor device is increased by the thickness of the molding portion 28. Therefore, there is a limit to the reduction of the height of the semiconductor device. When the substrate 10 and the substrate 12 are coupled to each other with the wire 30, it is necessary to keep a temperature of the wire-connecting pad 34 a given value by heating the substrate 10, the wire-connecting pad 34 being connected to the wire 30 of the substrate 12.
Here, generally, a thermal conductivity of the epoxy resin composing the molding portion 28 is lower than that of the silicon composing the semiconductor element 14. It is therefore difficult to conduct the heat from the substrate 10 to the wire-connecting pad 34 of the substrate 12 effectively when the substrate 10 and the substrate 12 are coupled to each other with the wire 30, in a case where the molding portion 28 is on the upper surface of the semiconductor element 14. It is difficult to connect the wire stably, and the yield ratio of the semiconductor device is reduced.
It is not possible to mount the built-in semiconductor device 48 horizontally, in a case where the height of the semiconductor element 14 is different from that of the semiconductor element 14a as is the case of the semiconductor device in accordance with the second conventional embodiment. This results in an inferior semiconductor device. Furthermore, the yield ratio of the semiconductor device gets reduced. It is possible to mount the built-in semiconductor device 48 horizontally by adjusting the thickness of the fixing portion 20, in a case where the height of the semiconductor element 14 is different from that of the semiconductor element 14a. In this case, however, the height of the semiconductor device increases, because the thickness of the fixing portion 20 gets larger by necessity.
Further, in the semiconductor device in accordance with the third conventional embodiment, the side surface of the semiconductor element 14 is exposed. Therefore, the risk of damaging the side surface of the semiconductor element 14 caused by an external impact increases in the previous mounting of the built-in semiconductor device 52. As a result, the yield ratio of the semiconductor device is reduced. In the semiconductor device disclosed in Document 1, it is possible to reduce the risk of damage to the side surface of the semiconductor element 14 caused by an external impact, because the molding portion protects the side surface of the semiconductor element. However, there is the same problem as the case of the first conventional embodiment in the semiconductor device disclosed in Document 1, because the upper surface of the semiconductor element is enclosed by the molding portion.